1. Field of the Invention
The present invention relates to an other-type fuel contamination determination apparatus for an internal combustion engine, which apparatus has a function of determining whether other-type fuel contaminates fuel that is supplied to the internal combustion engine.
2. Description of Related Art
A characteristic of fuel used for an internal combustion engine depends on an area or a season. For example, fuel having a large specific gravity or fuel having a small amount of low-boiling components is less likely to be volatile at a low temperature. JP-B-H06-15835 (for example, P.2) describes a system that executes an air-fuel ratio feed-back control for determining a final fuel supply amount by computing a feed-back correction amount of the fuel. The above feed-back correction amount of the fuel is computed so as to cause an air-fuel ratio of the exhaust gas detected by air-fuel ratio detection means to correspond to a target air-fuel ratio. In the above system, an average value of the final fuel supply amounts during the air-fuel ratio feed-back control is considered to be a specific gravity of fuel, and a fuel injection quantity during a cold operation, that is an open-loop control, for the internal combustion engine is corrected according to the specific gravity.
The internal combustion engine includes a gasoline engine that uses gasoline or a diesel engine that uses light oil. Recently, there have been constructed more self-service gas stations, where a driver refuels a vehicle by himself or herself. Therefore, the driver may supply light oil to a vehicle having the gasoline engine by mistake. In the above case, the light oil is other-type fuel that is not usable for the gasoline engine. Also, bad fuel, which is intentionally made by mixing other-type fuel into gasoline, may be supplied to the vehicle. In the above, the other-type fuel may be light oil or kerosene. In general, a specific gravity of gasoline, that is a fuel characteristic, may depend on the area or the season. Thus, a technique described in JP-B-H6-15835 (P.2) enables the vehicle to normally drive even when gasoline having the various specific gravities (fuel characteristic) is supplied to the vehicle having the gasoline engine.
In general, in a case, where other-type fuel (e.g., light oil, kerosene) or bad fuel is supplied to the vehicle having the gasoline engine, residual gasoline exists by some extent in a fuel tank. As a result, a recent electronic engine control system is able to operate the engine by an ignition timing control provided that contamination ratio of the other-type fuel relative to gasoline in the fuel tank is small. However, when the contamination ratio of the other-type fuel becomes larger, a combustion state of the engine deteriorates, and thereby, the engine rotation becomes unstable. Thus, in addition to the deterioration of the drivability, the engine may stop to disable the vehicle to run in a worst case scenario.
Even when other-type fuel or bad fuel is supplied in a state, where gasoline slightly exists in the fuel tank, gasoline in a fuel pipe from the fuel tank to the engine is supplied to the engine at an earlier stage. Thus, the engine may be normally operated for a while. Then, when it comes to a stage, were gasoline does not exist in the fuel pipe, and thereby other-type fuel or bad fuel is injected, the combustion state of the engine deteriorates causing the instability of the engine rotation. As a result, in a worst case scenario, the engine may stop to disable the vehicle to run disadvantageously.